While flap-type exhaust nozzles are well known in the jet engine art and several patents representing them are set forth below, no nozzle flap having a longitudinal series of louver elements was found; some of the nozzles show seal flaps which cooperate with the exhaust flow directing flaps to seal therebetween: U.S. Pat. Nos. 3,730,436; 3,792,815; 3,794,244; 3,820,720; 3,972,475; 3,979,065; 4,081,137; 4,456,178; and 4,544,098.